The SP6 was the first of the piston valved stationary engines introduced by Mamod.
The boiler is 1 3/4" diameter x 6" long and is fired by a large tablet burner. Boiler fittings include a water level sight glass, filler plug, safety valve and a banjo type steam connection. There is no whistle.
Steam is fed via a displacement lubricator and a needle valve to a very large brass steam chest. This communicates with the valve chest, containing a "piston" type valve. The cylinder is double acting, approx 3/8" bore x 1/2" stroke. The crankshaft has a disk crank and slip eccentric on one end, a 3" diameter spoked flywheel in the middle and a 7/16" diameter pulley.
The base has four holes - not Meccano compatible. It has a knock-out section which, presumably, is removed in the factory if the engine is supplied with the optional gas burner, or is removable by the user if the option is fitted later. There is a standard SP series chimney which, in this case, is a dummy and totally cosmetic.